The U.S. Department of Housing and Urban Development gives poor families a housing subsidy, and some people use that money to move to better neighborhoods. New social science research explores the effects of those Section 8 grants and finds something surprising in Houston. Our co-host Rachel Martin spoke about it with NPR's social science correspondent Shankar Vedantam.

RACHEL MARTIN, BYLINE: Hi, Shankar.

SHANKAR VEDANTAM, BYLINE: Hi, Rachel.

MARTIN: What's going on in Houston?

VEDANTAM: Well, there is a relationship between Section 8 grants and violent crime that we might not have expected. I was speaking with the economist Jillian Carr at Purdue University. Along with Vijetha Koppa, Carr has studied the effects of these housing grants in Houston. She told me she was hoping to find the vouchers were helping communities. But at least for a subset of recipients, she found something that she found very surprising.

JILLIAN CARR: We find a substantial increase in violent crime arrests due to voucher receipt. And this large increase is driven by men and those with a past criminal history. It's pretty substantial. We find an approximate doubling of violent crime arrests for this population.

MARTIN: So a doubling of crime among people who get these vouchers.

VEDANTAM: Well, two important things to keep in mind, Rachel - one, the doubling-in is largely driven by a subset of the recipients of the Section 8 grants. Most recipients of these grants are women. But the researchers find that the increase in violent crime is actually only among men who receive these vouchers and men with a prior criminal history and men who receive the vouchers but do not move to a new home. So that's...

MARTIN: Very specific subset of people.

VEDANTAM: Precisely.

MARTIN: So what does this tell us about a program where you are essentially giving money to people to help them with no strings attached. They can do with it what they will.

VEDANTAM: So an interesting quirk of the Section 8 program, Rachel, is it doesn't require people to move to another house. In other words, you can stay in your current house. And essentially for people who choose to do that, you have what economists call an income shock because now the voucher is essentially paying for your rent or your housing. And so you have money freed up for other things. Obviously many people who do that are probably going to use the money for good things.

MARTIN: Right.

VEDANTAM: But in any program where you're giving money to large numbers of people, some subset of the people are probably not going to use the money for good things.

MARTIN: Or even abuse the money or commit crimes with the money.

VEDANTAM: Precisely. In some ways, Rachel, I think this is true of any program. You know, if you're giving money or a voucher or a grant to large numbers of people - even if the large majority of people use the grant wisely, there are going to be some people who don't use it wisely. There has been some research looking at Social Security benefits, for example, that find a subset of recipients are more likely to end up in the emergency room after they receive their benefits with drug-related problems.

MARTIN: So what's the upshot of this? I mean, what does it mean that some people use these federal programs for good and some people don't?

VEDANTAM: I think with any public policy program, Rachel, it's really useful to see where it's working well and where it's not working well. I think we often assume that just because a program works well in one context, it's going to work well in another context. And I think what this research is showing us is that at least in the city of Houston, the program's not working as intended for this subgroup of people.

What we don't know is, does this result extrapolate to other cities in the United States? But what it tells us is we would be really wise to measure the outcomes in each city that we're applying this program and then try and tailor the program so we can get the good outcomes without the bad.

MARTIN: Shankar Vedantam - he's NPR's social science correspondent and the host of a podcast and a radio show, both called Hidden Brain. Thanks, Shankar.